Device containing non-blinking quantum dots

ABSTRACT

An optoelectronic device including two spaced apart electrodes; and at least one layer containing ternary core/shell nanocrystals disposed between the spaced electrodes and having ternary semiconductor cores containing a gradient in alloy composition and wherein the ternary core/shell nanocrystals exhibit single molecule non-blinking behavior characterized by on times greater than one minute or radiative lifetimes less than 10 ns.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under CooperativeAgreement #DE-FC26-06NT42864 awarded by DOE. The Government has certainrights in this invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned U.S. patent application Ser. No.11/226,622 filed Sep. 14, 2005, entitled “Quantum Dot Light EmittingLayer” by Keith B. Kahen; U.S. patent application Ser. No. 11/683,479filed Mar. 8, 2007, entitled “Quantum Dot Light Emitting Device” byKeith B. Kahen; U.S. patent application Ser. No. 11/770,8334 filed Jun.29, 2007, entitled “Light-Emitting Nanocomposite Particles” by Keith B.Kahen and U.S. patent application Ser. No. 11/926,538 filed Oct. 29,2007, entitled “Making Colloidal Ternary Nanocrystals” by Keith B. Kahenet al, the disclosures of which are incorporated herein.

FIELD OF THE INVENTION

The present invention relates to applications using non-blinkingnanocrystals, and particularly to non-blinking core/shell nanocrystalswith ternary cores of CdZnSe.

BACKGROUND OF THE INVENTION

Colloidal semiconductor nanocrystals, or quantum dots, have been thefocus of a lot of research. Colloidal quantum dots, hereto withinreferred to as quantum dots or nanocrystals, are easier to manufacturein volume than self-assembled quantum dots. Colloidal quantum dots canbe used in biological applications since they are dispersed in asolvent. Additionally, the potential for low cost deposition processesmake colloidal quantum dots attractive for light emitting devices, suchas LEDs, as well as other electronic devices, such as, solar cells,lasers, and quantum computing devices. While potentially broader intheir applicability than self-assembled quantum dots, colloidal quantumdots do have some attributes that are comparatively lacking. Forexample, self-assembled quantum dots exhibit relatively short radiativelifetimes, on the order of 1 ns, while colloidal quantum dots typicallyhave radiative lifetimes on the order of 20-200 ns. Colloidal quantumdots also exhibit blinking, characterized by a severe intermittency inemission, while self-assembled quantum dots do not have thischaracteristic.

Of particular interest are II-VI semiconductor nanocrystals. Thesenanocrystals have size-tunable luminescence emission spanning the entirevisible spectrum. In photoluminescent applications, a single lightsource can be used for simultaneous excitation of different-sized dots,and their emission wavelength can be continuously tuned by changing theparticle size. Since they are also able to be conjugated tobiomolecules, such as, proteins or nucleic acids, this photoluminescenceproperty makes them an attractive alternative for organic fluorescentdyes classically used in biomedical applications. Additionally, thetunable nature of the emission makes quantum dots well suited for fullcolor display applications and lighting. As a result of theirwell-established high-temperature organometallic synthetic methods(Murray et al, J. Am. Chem. Soc. 115, 8706-8715 1993) and theirsize-tunable photoluminescence (PL) across the visible spectrum, CdSenanocrystals have become the most extensively investigated quantum dots(QD).

As noted by Hohng et al (J. Am. Chem. Soc. 126 1324-1325 (2004)),colloidal semiconductor quantum dots are also brighter and far morephotostable than organic dyes, making them particularly interesting forbiological applications. It also has been reported in the openliterature that surface passivation of quantum dots with a semiconductorlayer having a wider band gap or with polymers improves the opticalproperties of quantum dots, such as, quantum yield and photobleaching.The blinking behavior of quantum dots, however, is generally consideredan intrinsic limitation that is difficult to overcome. This isunfortunate because growing applications in spectroscopy of singlebiological molecules and quantum information processing usingsingle-photon sources could greatly benefit from long-lasting andnonblinking single-molecule emitters. For instance, in a recentapplication of single-dot imaging, the tracking of membrane receptorswas interrupted frequently due to the stroboscopic nature of recording.Blinking can also reduce the brightness in ensemble imaging via signalsaturation. Furthermore, blinking limits the use of colloidal quantumdots in luminescent applications such as single molecule LEDs.

A few groups have been working on solutions to the colloidal quantum dotblinking problem, especially for biological applications. It was foundin 2004 by Hohng et al (Hohng et al., J. Am. Chem. So. 126, 1324-1325(2004)) that quantum dot blinking could be suppressed by passivating theQD surface with thiol moieties. The experiments by Hohng et al wereconducted with CdSe/ZnS quantum dots that showed inherent blinkingbehavior. Larson et al studied encapsulating the QDs within anamphiphilic polymer (Larson, et al., Science 300, 1434-1435, 2003),using water soluble CdSe/ZnS QDs. The results of Hohng et al and Larsonet al do not solve the intrinsic problems resulting in blinking dots,they only control the environment at the surface of the dots in order tomitigate the problem. Both approaches are only useful in endapplications that remain in solution and allow particular surfacepassivations.

In addition to the problem of blinking, colloidal quantum dots sufferfrom increased radiative lifetimes as compared with their self-assembledcounterparts. Radiative lifetime is defined as the reciprocal of thefirst-order rate constant for the radiative step, or the sum of theserate constants if there is more than one such step (IUPAC Compendium ofChemical Terminology, 2^(nd) Edition (1997)). Short radiative lifetimesare desirable in order to compete successfully with non-radiativerecombination events, such as, Forster energy transfer.

Although quantum dots containing CdSe cores are arguably the moststudied and best understood of the quantum dots, some researchers arelooking at more complex quantum dots with ternary rather than binarycompositions. U.S. Pat. No. 7,056,471 by Han et al discloses processesand uses of ternary and quaternary nanocrystals (quantum dots). Thenanocrystals described by Han et al are not core/shell quantum dots,rather they are homogeneously alloyed nanocrystals (also referred to asnanoalloys). Although Han et al do not address the issue of blinking intheir disclosure, Stefani et al us use nanoalloy dots made by thedisclosed process for a study of photoluminescence blinking (Stefani etal, New Journal of Physics 7, 197 (2005)). Stefani et al found thatmonocrystalline Zn_(0.42)Cd_(0.58)Se QDs with an average diameter of 6.2nm exhibited pholuminescence blinking. Although Stefani et al do notdiscuss the radiative lifetimes of their ternary nanocrystals, Lee et alhave studied colloidal ternary ZnCdSe semiconductor nanorods (Lee et al,Journal of Chemical Physics 125, 164711 (2006)). Lee et al found thatthe ternary nanorods exhibit radiative lifetimes slightly longer thancomparable CdSe/ZnSe core/shell nanorods. The CdSe/ZnSe nanorods hadlifetimes around 173 ns, while the shortest lifetime for the ternaryrods was observed to be 277 ns.

While researches in biological fields are looking to quantum dots toreplace organic fluorescent dyes, quantum dots also hold promise for usein electronic devices. Research is ongoing into incorporating quantumdots into photovoltaics, solid-state lighting (mainly as quantum dotphosphors), electroluminescent displays as well as quantum computingdevices. Semiconductor light emitting diode (LED) devices have been madesince the early 1960s and currently are manufactured for usage in a widerange of consumer and commercial applications. The layers including theLEDs are based on crystalline semiconductor materials that requireultra-high vacuum techniques for their growth, such as, metal organicchemical vapor deposition. In addition, the layers typically need to begrown on nearly lattice-matched substrates in order to form defect-freelayers. These crystalline-based inorganic LEDs have the advantages ofhigh brightness (due to layers with high conductivities), longlifetimes, good environmental stability, and good external quantumefficiencies. The usage of crystalline semiconductor layers that resultsin all of these advantages, also leads to a number of disadvantages. Thedominant ones are high manufacturing costs, difficulty in combiningmulti-color output from the same chip, and the need for high cost andrigid substrates.

In the mid 1980s, organic light emitting diodes (OLED) were invented(Tang et al, Appl. Phys. Lett. 51, 913 (1987)) based on the usage ofsmall molecular weight molecules. In the early 1990s, polymeric LEDswere invented (Burroughes et al., Nature 347, 539 (1990)). In theensuing 15 years organic based LED displays have been brought out intothe marketplace and there has been great improvements in devicelifetime, efficiency, and brightness. For example, devices containingphosphorescent emitters have external quantum efficiencies as high as19%; whereas, device lifetimes are routinely reported at many tens ofthousands of hours. In comparison to crystalline-based inorganic LEDs,OLEDs have much reduced brightness (mainly due to small carriermobilities), shorter lifetimes, and require expensive encapsulation fordevice operation. On the other hand, OLEDs enjoy the benefits ofpotentially lower manufacturing cost, the ability to emit multi-colorsfrom the same device, and the promise of flexible displays if theencapsulation issues can be resolved.

To improve the performance of OLEDs, in the later 1990s OLED devicescontaining mixed emitters of organics and quantum dots were introduced(Matoussi et al., J. Appl. Phys. 83, 7965 (1998)). The virtue of addingquantum dots to the emitter layers is that the color gamut of the devicecould be enhanced; red, green, and blue emission could be obtained bysimply varying the quantum dot particle size; and the manufacturing costcould be reduced. Because of problems, such as, aggregation of thequantum dots in the emitter layer, the efficiency of these devices wasrather low in comparison with typical OLED devices. The efficiency waseven poorer when a neat film of quantum dots was used as the emitterlayer (Hikmet et al., J. Appl. Phys. 93, 3509 (2003)). The poorefficiency was attributed to the insulating nature of the quantum dotlayer. Later the efficiency was boosted (to ˜1.5 cd/A) upon depositing amonolayer film of quantum dots between organic hole and electrontransport layers (Coe et al., Nature 420, 800 (2002)). It was statedthat luminescence from the quantum dots occurred mainly as a result ofForster energy transfer from excitons on the organic molecules(electron-hole recombination occurs on the organic molecules).Regardless of any future improvements in efficiency, these hybriddevices still suffer from all of the drawbacks associated with pure OLEDdevices.

Recently, a mainly all-inorganic LED was constructed (Mueller et al.,Nano Letters 5, 1039 (2005)) by sandwiching a monolayer thick core/shellCdSe/ZnS quantum dot layer between vacuum deposited n- and p-GaN layers.The resulting device had a poor external quantum efficiency of 0.001 to0.01%. Part of that problem could be associated with the organic ligandsof trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP) that werereported to be present post growth. These organic ligands are insulatorsand would result in poor electron and hole injection into the quantumdots. In addition, the remainder of the structure is costly tomanufacture, due to the usage of electron and hole semiconducting layersgrown by high vacuum techniques, and the usage of sapphire substrates.

Accordingly, it would be highly beneficial to construct an all inorganicLED based on quantum dot emitters which was formed by low costdeposition techniques and whose individual layers showed goodconductivity performance. The resulting LED would combine many of thedesired attributes of crystalline LEDs with organic LEDs.

For solid state lighting applications, the fastest route to highefficiency white LEDs is to combine either blue, violet, or near UV LEDswith appropriate phosphors. Replacing traditional optically pumpedphosphors with quantum dot phosphors has many advantages, such as,greatly reduced scattering, ease of color tuning, improved colorrendering index (CRI), lower cost deposition process, and broaderwavelength spectrum for optical pumping. Despite these advantages,quantum dot phosphors have not been introduced into the marketplace dueto some major shortcomings; such as, poor temperature stability andinsufficient (10-30%) quantum yields for phosphor films with highquantum dot packing densities. In order to raise the quantum yield, manyworkers have lowered the packing density by incorporating appropriatefiller (e.g., polymers or epoxies) with the quantum dots. Thedisadvantage of this approach is that the resulting quantum dot phosphorfilms are unacceptably thick (1 mm), as compared to the desiredthickness of 10 μm. As has been discussed by Achermann et al (Achermannet al., Nano Lett 6, 1396 (2006)), reduced quantum yields for densefilms is mainly the result of inter-nanoparticle interactions that leadto exciton transfer (Forster energy transfer) from emitting quantum dotsto non-emitting quantum dots. Since the Forster energy transfer ratedecreases rapidly with distance, d, as 1/d⁶, a way to minimize thiseffect is to form low density films (with the aforementioned problems).A more desirable approach would be to decrease the radiative lifetime ofthe quantum dot emitters in order to compete more effectively with theForster energy process, while enabling dense films of quantum dotphosphors. More specifically, the Forster energy transfer time for dropcast films of quantum dots has been experimentally measured to be on thenanosecond time scale (Achermann et al., J. Phys. Chem. B107, 13782(2003)).

To date, optoelectronic devices or biological studies have not hadcolloidal quantum dots available that are inherently non-blinking orthat have short radiative lifetimes. Previous methods to createnon-blinking dots are application dependent and not universallyapplicable across the technical disciplines utilizing quantum dots.While self-assembled quantum dots exhibit short radiative lifetimes,there are no reports of colloidal quantum dots exhibiting similarperformance. Therefore, there is a need for colloidal quantum dots withinherent non-blinking behavior for use in biological and electronicsapplications. Additionally, there is a need for quantum dots with shortradiative lifetimes that could be used in biological and optoelectronicsapplications.

SUMMARY OF THE INVENTION

It is an object of this invention to provide non-blinking core/shellternary quantum dots for use in medical, biological, quantum computing,quantum cryptography, lighting and display applications.

This object is achieved by an optoelectronic device comprising:

(a) two spaced apart electrodes; and

(b) at least one layer containing ternary core/shell nanocrystalsdisposed between the spaced electrodes and having ternary semiconductorcores containing a gradient in alloy composition and wherein the ternarycore/shell nanocrystals exhibit single molecule non-blinking behaviorcharacterized by on times greater than one minute or radiative lifetimesless than 10 ns.

This object is further achieved by an inorganic light emitting deviceincluding a plurality of independently controlled light emittingelements, wherein at least one light emitting element comprises: a firstpatterned electrode; a second electrode opposed to the first electrode;and a polycrystalline inorganic light emitting layer comprising ternarycore/shell nanocrystals within a semiconductor matrix formed between theelectrodes, wherein the ternary core/shell nanocrystals have ternarysemiconductor cores containing a gradient in alloy composition andexhibit single molecule non-blinking behavior characterized by on timesgreater than one minute or radiative lifetimes less than 10 ns.

This object is further achieved by a single photon optoelectronic devicecomprising two spaced apart electrodes; and a single ternary core/shellnanocrystal disposed between the two spaced apart electrodes and havinga ternary semiconductor core containing a gradient in alloy compositionand exhibiting single molecule non-blinking behavior characterized by ontimes greater than one minute or radiative lifetimes less than 10 ns.

This object is further achieved by an optical device comprising at leastone layer containing ternary core/shell nanocrystal(s) wherein theternary core/shell nanocrystal(s) have ternary semiconductor corescontaining a gradient in alloy composition and exhibit single moleculenon-blinking behavior characterized by on times greater than one minuteor radiative lifetimes less than 10 ns; and a light source for opticallyexciting the ternary core/shell nanocrystal(s) so as to cause emissionof light from the ternary core/shell nanocrystal(s).

This object is further achieved by a system including a marker actuableby radiation and used to detect a given analyte, comprising a ternarycore/shell nanocrystal, having a ternary semiconductor core containing agradient in alloy composition and exhibiting single moleculenon-blinking behavior characterized by on times greater than one minuteor radiative lifetimes less than 10 ns; and a molecule conjugated withthe ternary core/shell nanocrystal and having a binding affinity for theanalyte.

It is an advantage of the present invention that the non-blinkingproperty of the ternary core/shell nanocrystals is not limited by typeof solvent or type of surface ligands on the shell. This permits thenanocrystals to remain non-blinking in many environments andapplications. It is an important feature of the invention that theternary semiconductor cores have a gradient in alloy composition inorder to achieve the non-blinking and short radiative lifetimeproperties. It is also an advantage that the ternary core/shellnanocrystals have much reduced radiative lifetimes compared to typicalnanocrystals which enables enhanced quantum dot phosphor films, moreefficient conventional LED devices, and single photon LED devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a ternary core/shell nanocrystal of thepresent invention;

FIG. 2 shows examples of biological labels composed of ternarycore/shell nanocrystals in accordance with the present invention;

FIG. 3 shows a side-view schematic of a light emitting device inaccordance with the present invention;

FIG. 4 shows a schematic of a section of an inorganic light emittinglayer in accordance with the present invention;

FIG. 5 shows a side-view schematic of another embodiment of a lightemitting device in accordance with the present invention;

FIG. 6 shows an example of a passive matrix electroluminescent (EL)device in accordance with the present invention;

FIG. 7 shows a pixel layout of a bottom emitting electroluminescentdevice in accordance with the present invention;

FIG. 8 shows a cross section of a bottom emitting electroluminescentdevice in accordance with the present invention;

FIG. 9 shows a cross section of a top emitting electroluminescent devicein accordance with the present invention;

FIG. 10 shows TEM images of ternary core/shell nanocrystals of thepresent invention;

FIG. 11 shows a STEM image of a ternary core/shell nanocrystal of thepresent invention;

FIGS. 12A and 12B show fluorescence time traces of the ternarycore/shell nanocrystals of the present invention;

FIG. 13 shows the fluorescence time trace of a conventional nanocrystalrepresentative of the prior art; and

FIGS. 14A and 14B shows the second-order correlation functions, g⁽²⁾(τ),for ternary core/shell nanocrystals of the present invention and forconventional prior art nanocrystals.

DETAILED DESCRIPTION OF THE INVENTION

As discussed above in the background section, it is advantageous tocreate nanocrystals (or quantum dots) that don't blink and have shortradiative lifetimes. Single molecule blinking is initiated (M. Nirmal etal., Nature 383, 802 (1996)) when a nanocrystal is excited bymultiphotons and two or more electron-hole pairs are created. Instead ofthe energy being released radiatively, one of the pairs loses its energyby Auger recombination and transfers its energy to one of the remainingelectrons or holes. The excited electron or hole can then be ejectedfrom the nanocrystal into the surrounding matrix. In the resultingionized nanocrystal, the Auger recombination process dominates overradiative recombination and the nanocrystal remains dark in spite ofcontinual excitation. The nanocrystal will remain dark until the ejectedcarrier finds its way (via tunneling, for example) back into thenanocrystal and returns the nanocrystal to the uncharged state. As canbe seen by this phenomenological model, blinking could be reduced orstopped by preventing the ejection of a carrier from the nanocrystalinterior. Forming a very thick semiconductor shell (as forself-assembled quantum dots) is the straightforward solution, however,implementing this in practice is difficult since defect formation in theshell (due to lattice mismatch) scales with shell thickness. Ananocrystal with defects in its shell would not only blink (since chargecan be trapped at the defects), but would also exhibit a reduced quantumefficiency. Thus, one needs to seek different ways for keeping thecarriers confined within the nanocrystal volume and away from thesurface. One can see that by engineering a nanocrystal where theelectrons and holes are more tightly confined to the center region (andaway from the surface), that this will also lead to a reduction in theelectron and hole radiative lifetime as a result of the Purcell effect.

It is well known that as a result of Anderson localization (P. Anderson,Phys. Rev. 109, 1492 (1958)), even slight randomization of atomicpositions (15%) or atomic energy levels will lead to localization ofcharge carriers in a material. Semiconductor substitutional alloysexhibit random variations in the atomic energy levels, and as such,manifest charge localization effects (E. Economou et al., Phys. Rev.Lett. 25, 520 (1970). Given this result, a hypothesized scenario forcarrier localization in a nanocrystal would be to create a nanocrystalwith an ordered core center, a random alloy middle shell, and an orderedouter shell. The ordered outer shell is added to ensure that theelectron and holes remain confined to the core and middle shell region.A way for creating this designer nanoparticle is discussed below.

Typically, ternary semiconductor alloy nanocrystals are created byadding, at the start of the synthesis, appropriate ratios of cations(e.g., CdZnSe) or anions (CdSeTe) into the synthesis reaction mixture(R. Bailey et al., JACS 125, 7100 (2003)). This procedure would normallyresult in an alloy homogenously distributed throughout the nanocrystalvolume. Taking the example of the CdZnSe system, in order to form arandom alloy middle shell, a more appropriate scheme would be toinitially create a CdSe core, shell it with ZnSe, and then perform anappropriate anneal. As is well known in the art, the diffusion profilewould be such that the maximum Zn concentration in the nanocrystal wouldoccur at the surface, while in the core center the Zn content would bemuch lower (CdZnSe, but with a high Cd/Zn ratio). Given the weakening Znpenetration into the center of the nanocrystal, the surface region ofthe annealed nanoparticle would show the strongest random alloyattributes, with the core region behaving mainly as crystalline CdSe. Assuch, e-h pairs present in the core CdSe-like region would not only getlocalized by the increasing energy gap of the CdZnSe surface region, butalso by carrier localization generated by the band of random alloysurrounding the core region of the nanocrystal. As stated above an extraouter shell of wide bandgap material, such as, ZnSeS or ZnS, could beadded to the annealed nanostructure in order to ensure carrierconfinement to the core and middle shell (containing the CdZnSe randomalloy) regions.

A more general description of the present invention is ternarysemiconductor nanocrystals 100 that have a gradient in the alloycomposition from the surface of the ternary nanocrystal to the center ofthe ternary nanocrystal. In a ternary center region 145 of the ternarysemiconductor nanocrystal 100, the degree of alloying can be low suchthat the semiconductor material is largely binary in composition.Between the ternary center 145 and a ternary surface 135 regions thereis an alloy composition transition region where the alloy compositionchanges from its ternary center composition (mainly binary) to itsternary surface composition (ternary random alloy). To enable greaterconfinement of the electrons and holes, a semiconductor shell 110 (ormultiple shells) can be added to the ternary semiconductor nanocrystals100 (with a gradient in alloy composition) resulting in the formation ofternary core/shell nanocrystals 120. The ternary semiconductornanocrystal (either core, core/shell, or core with multiple shells) canbe a nanodot, a nanorod, a nanowire, a nano-tetrapod, or any otherhigher dimensional nanoscale particle that shows quantum confinementeffects. With regard to material content, the ternary semiconductornanocrystal 100 can include II-VI, III-V, or IV-VI semiconductivematerials; some examples of ternary semiconductive materials are CdZnSe,CdZnS, InGaAs, and PbSeS, respectively. The semiconductor shell(s) 110material of the ternary core/shell nanocrystals 120 can be composed ofII-VI, III-V, or IV-VI semiconductive materials; however, it ispreferred that the semiconductor shell 110 material be II-VIsemiconductive material since, to date, successful nanocrystal shellinghas only been performed with II-VI materials. The (multiple)semiconductor shell 110 material can either be a binary, ternary, orquaternary compound, for example, ZnSe, CdS, ZnS, ZnSeS, or CdZnSeS.Attached to the surfaces of the ternary core/shell nanocrystals 120 areorganic ligands 115, which aid in the nanocrystal growth process andhelp to stabilize the nanocrystals in the resulting colloids. Specificmethods for creating these ternary core/shell nanocrystals 120, alongwith data showing their single molecule non-blinking (on times greaterthan a few hours) and short radiative lifetime (4-5 ns) characteristics,will be given below in the examples section. In summary, ternarycore/shell nanocrystals 120 are formed, wherein the ternarysemiconductor cores contain a gradient in alloy composition, resultingin single molecule non-blinking behavior characterized by on timesgreater than one minute or radiative lifetimes less than 10 ns.

As discussed above with reference to the CdZnSe ternary semiconductornanocrystal 100, the diffusion profile of Zn (from the ZnSe shell) wouldbe such that the maximum Zn concentration in the nanocrystal would occurin the ternary surface region 135, while in the ternary center region145 the Zn content would be much lower (CdZnSe, but with a high Cd/Znratio). As will be discussed in the example section below, an unexpectedconsequence of this profile (for the CdZnSe system) is that theunderlying lattice structure changes from wurtzite in the ternary centerregion 145 to cubic (or zincblende) in the ternary surface region 135.Between the ternary center region 145 and ternary surface region 135,there is a lattice transition region where the lattice evolves fromwurtzite to zincblende. One can account for this lattice structureevolution by noting that in the ternary center region 145 where theCdZnSe has a high Cd/Zn ratio, the lattice structure should reflect thatof CdSe nanocrystals at room temperature, namely wurtzite.Correspondingly, in the ternary surface region 135, where the Cd/Znratio in CdZnSe is smaller than 1 (and possibly much smaller than 1),the lattice structure should reflect that of ZnSe nanocrystals at roomtemperature, namely zincblende. The physical consequence of the latticestructure change from ternary center region 145 to ternary surfaceregion 135 is that it enhances the localization of the charge carriersto the ternary center region 145. Phenomenologically the addedlocalization can be understood based on the following. Placing anelectron in the wurtzite ternary center region 145, as it propagatesoutward in the core and begins to cross into the zincblende ternarysurface region 135, the electron wave would scatter due to the change inthe lattice structure (as stated above, even a small 15% randomvariation in lattice position causes Anderson localization). It shouldbe noted that this extra confinement due to a change in latticestructure will only occur if the two binary components of the ternaryalloy have different room temperature lattice structures. For the commonII-VI binary compounds, CdSe and CdS form wurtzite nanocrystals, whileCdTe, ZnS, ZnSe, and ZnTe form zincblende nanocrystals. Accordingly asexamples, the ternary CdZnS would show a lattice change, while ZnSeTewould not. For the case of annealing CdTe/CdS core/shell nanocrystals,interdiffusion on the anion sublattice would be hypothesized to lead toa zincblende lattice in the ternary center region 145 and a wurtzitelattice in the ternary surface region 135.

Combining all of the above, confinement of the carriers in the ternarycenter region 145 of the invented ternary nanocrystal is hypothesized tooccur as a result of three phenomena brought on by the diffusionprofile: 1). The energy gap of the ternary surface region 135 is largerthan that of the ternary center region 145 (typical cause ofconfinement); 2) Anderson localization due to more significant randomalloy formation in the ternary surface region 135 compared to that inthe ternary center region 145; and 3) Scattering localization due to adifference in lattice structure between the ternary center region 145(for example, wurtzite) and the ternary surface region 135 (for example,zincblende).

The present invention further refers to a ternary core/shell quantum dot(or nanocrystal), as disclosed here, conjugated to a molecule havingbinding affinity for a given analyte. By conjugation to a moleculehaving binding affinity for a given analyte, a marker compound or probeis formed in which the nanocrystal of the invention serves as a label ortag which emits radiation, preferably in the visible or near infraredrange of the electromagnetic spectrum, that can be used for thedetection of a given analyte. FIG. 2 gives an illustration of quantumdots being used to tag a protein. In the figure, a analyte 510 is aprotein, a binding partner 505 is an antibody, and the fluorescent tagsare non-blinking ternary core/shell quantum dots 120. For thisinvention, the excitation radiation can be UV, visible, or infraredlight; whereas, the radiation emitted by the invented ternary core/shellnanocrystals 120 can also be UV, visible, or infrared light but of alonger corresponding wavelength. The invention further includes a mediumcontaining a given analyte; a marker composed of a molecule conjugatedto the invented ternary core/shell nanocrystals 120 and having bindingaffinity for the given analyte; a light source for illuminating themarker with radiation that causes the emission of light from theconjugated ternary core/shell nanocrystal; and a detection apparatus foranalyzing the emitted radiation in order to determine the presence ofthe analyte.

In principle every analyte can be detected for which a specific bindingpartner exists that is able to at least somewhat specifically bind tothe analyte. The analyte can be a chemical compound such as a drug (e.g.Aspirin® or Ribavirin), or a biochemical molecule such as a protein (forexample troponin) or a nucleic acid molecule. When coupled to anappropriate molecule with binding affinity (which is also referred to asthe analyte binding partner) for an analyte of interest, such asRibavirin, the resulting probe can be used for example in a fluorescentimmunoassay for monitoring the level of the drug in the plasma of apatient. In case of troponin, which is a marker protein for damage ofthe heart muscle, and thus in general for a heart attack, a conjugatecontaining an anti-troponin antibody and an inventive nanocrystal can beused in the diagnosis of a heart attack.

The analyte can also be a complex biological structure including but notlimited to a virus particle, a chromosome or a whole cell. For example,if the analyte binding partner is a lipid that attaches to a cellmembrane, a conjugate including a nanocrystal of the invention linked tosuch a lipid can be used for detection and visualization of a wholecell. For purposes, such as, cell staining or cell imaging, ananocrystal emitting visible light is preferably used. In accordancewith this disclosure the analyte that is to be detected by use of amarker compound, that includes a nanoparticle of the inventionconjugated to an analyte binding partner, is preferably a biomolecule.

Therefore, in a further preferred embodiment, the molecule havingbinding affinity for the analyte is a protein, a peptide, a compoundhaving features of an immunogenic hapten, a nucleic acid, a carbohydrateor an organic molecule. The protein employed as analyte binding partnercan be, for example, an antibody, an antibody fragment, a ligand,avidin, streptavidin or an enzyme. Examples of organic molecules arecompounds, such as, biotin, digoxigenin, serotronin, folate derivativesand the like. A nucleic acid can be selected from, but not limited to, aDNA, RNA or PNA molecule, a short oligonucleotide with 10 to 50 bp aswell as longer nucleic acids.

When used for the detection of biomolecules a ternary-core/shellnanocrystal of the invention can be conjugated to the molecule havingbinding activity for an analyte via a linking agent. A linking agent asused herein, means any compound that is capable of linking aternary-core/shell nanocrystal of the invention to a molecule havingsuch binding affinity. Examples of the types of linking agents which maybe used to conjugate a nanocrystal to the analyte binding partner are(bifunctional) linking agents such as ethyl-3-dimethylaminocarbodiimideor other suitable cross-linking compounds which are known to personsskilled in the art. Examples of suitable linking agents areN-(3-aminopropyl)-3-mercapto-benzamide, 3-aminopropyl-trimethoxysilane,3-mercaptopropyl-trimethoxysilane, 3-(trimethoxysilyl)propylmaleimide,and 3-(trimethoxysilyl)propyl-hydrazide. Prior to reaction with thelinking agent, the surface of the nanocrystals can be modified, forexample, by treatment with glacial mercaptoacetic acid, in order togenerate free mercaptoacetic groups which can then be employed forcovalently coupling with an analyte binding partner via linking agents

The markers formed in which the nanocrystal of the invention serves as alabel or tag, in accordance with the embodiments, can have applicationsin a wide variety of fields. Many of the markers are intended for use inthe fields of biology and medicine. For example, by conjugation toantibodies, the markers described herein can be used routinely for thedetection of proteins in cells (immunocytochemistry) and tissues(immunohistochemistry), for nucleic acid detection by fluorescentin-situ hybridization (FISH) and for detecting bacteria and viruses.They also provide a reliable tool for the visualization and mapping ofmRNA, DNA expression patterns in various specimens, and for antibody-and antigen-based array studies and detection of antigen-antibodyinteractions. Furthermore, these markers can also enable detection oftrace amounts of toxins in food and other consumer end products.

The ternary core/shell quantum dot (or nanocrystal)-based markers asdescribed herein can be applied in both in vitro and in vivo analysis.For example, they may be used as noninvasive measures in vivo toidentify cancer signatures, monitor drug delivery, evaluate drug-inducedeffects in tumors, and monitor the spatial and temporal distribution ofcancer drugs within tumors that may allow for more effective and precisedosing.

Different signal enhancing approaches are applicable to the markers asdescribed herein. For example, the surfaces of the markers can beengineered such that multiple markers are accumulated on one targetanalyte, resulting in an increase in the intensity of fluorescence.Another example is the indirect immunoassay technique, where the analyteis targeted by a primary antibody, while the bound primary antibody isvisualized by a secondary antibody. The signal detection techniquesinclude, but are not limited to, one- and two-photon steady-state andtime resolved fluorescence.

In one preferred embodiment, the nanocrystal is incorporated into aplastic bead or a latex bead. Furthermore, a detection kit containingthe inventive nanocrystals as defined here is also part of theinvention.

In addition to the above described biomedical applications asfluorescent probes, the ternary-core/shell quantum dots of the presentinvention can also be used in light-emitting devices and quantuminformation (computing and cryptography) devices. For light emittingdevice applications, emission from the ternary-core/shell quantum dotscan occur as a result of direct electron-hole recombination on the dots,Forster energy transfer from neighboring emissive species (both organicand inorganic), and optically pumping from a variety of light sources,such as, inorganic LEDs, organic LEDs, lasers, and compact fluorescentlamps. Forster energy transfer mediated light emission from quantum dotsembedded in LED devices has been discussed for both OLEDs (Coe et al.,Nature 420, 800 (2002)) and LEDs (Achermann et el., Nano Lett 6, 1396(2006)). Both types of LED devices will be enhanced as a result ofemploying the ternary-core/shell quantum dots of the present invention.More specifically, it is desirable that radiative recombination occursas soon as the exciton has been transferred (via Forster energytransfer) to the quantum dot in order to prevent unwanted nonradiativerecombination from occurring. Since the ternary core/shell quantum dotshave short radiative lifetimes, nonradiative recombination will bereduced, resulting in LED devices with overall higher internal quantumefficiencies.

Another application for incorporating emissive quantum dots in lightemitting devices is to employ them as emissive phosphors that areoptically pumped by a higher energy (the wavelength of the pump sourceis shorter than the average emission wavelength) light source. Inventiveoptically pumped devices of the present invention contain at least onelayer having the ternary core/shell nanocrystals and a light source forexciting the nanocrystals, which causes the ternary core/shellnanocrystals to emit light. The light source can be an LED (eitherorganic or inorganic), a laser, a compact fluorescent lamp, or any otherincoherent light source that is well known in the art. The phosphors, orternary core/shell nanocrystals, can be used to produce white light,convert higher energy light into a specific visible wavelength band (forexample, produce green light), or any other desired wavelengthconversion (emit ultraviolet, blue, cyan, green, yellow, magenta, red,or infrared radiation, or a combination thereof) as is well known in theart. As discussed above, there are many advantages to replacingconventional phosphors by quantum dot phosphors; however, their usage inproduct is hampered by their poor temperature performance and lowquantum efficiency in dense quantum dot phosphor films. Since, asdiscussed above, the later deficiency can be remedied by employingemissive quantum dots with short radiative lifetimes, using the ternarycore/shell quantum dots of the present invention as phosphors willenable enhanced quantum efficiencies as a result of their shortradiative lifetimes.

The final category of light emitting devices incorporating quantum dotsare those for which emission occurs as a result of direct recombinationof electron and holes inside of the dots. Again, the internal quantumefficiency (IQE) of the LED or laser will be enhanced as a result ofincorporating the ternary core/shell quantum dots of the presentinvention (with short radiative lifetimes) as the emissive quantum dotsin the device. As is well known in the optoelectronic device art, shortradiative lifetimes following electron-hole injection result in enhanceddevice IQE, thus explaining the enhanced IQE of laser and microcavityLED devices.

In the illustration in FIG. 3, a typical LED 11 structure is shown toaide in the understanding electroluminescent device embodiments of thecurrent invention. LED 11 contains an electroluminescent (EL) unit 15between a first electrode 17 and a second electrode 20. The EL unit 15as illustrated contains all layers between the first electrode 17 andthe second electrode 20, but not the electrodes. A light-emitting layer33 includes light-emitting ternary-core/shell nanocrystals 120 in asemiconductor matrix 31. Semiconductor matrix 31 can be an organic hostmaterial in the case of hybrid LED devices, or an inorganicsemiconductor matrix that is either crystalline or polycrystalline inthe case of inorganic quantum dot LEDs. The light-emitting layer 33 canbe considered to contain an ensemble of quantum dots, referring to thefact that there are multiple quantum dots in the emitter layer 33 thatemit light. Since the radiative lifetime is short for each of these QDs,the overall efficiency of LEDs using an ensemble of these quantum dotswill be improved over traditional quantum dots. Although thelight-emitting layer 33 is illustrated as having the light-emittingternary core/shell nanocrystals 120 well dispersed within thesemiconductor matrix 31, this is for illustration purposes only andshould not be considered limiting. The ternary core/shell nanocrystals120 can also be in a single layer, or monolayer. EL unit 15 canoptionally contain p-type or n-type charge transport layers 35 and 37,respectively, in order to improve charge injection. EL unit 15 can haveadditional charge transport layers, or contact layers (not shown). Onetypical LED device uses a glass substrate, a transparent conductinganode such as indium-tin-oxide (ITO), an EL unit 15 containing a stackof layers, and a reflective cathode layer. The layers in the EL unit 15can be organic, inorganic, or a combination thereof. Light generatedfrom the device is emitted through a glass substrate 10. This iscommonly referred to as a bottom-emitting device. Alternatively, adevice can include a non-transparent substrate, a reflective anode, astack of layers (organic, inorganic, or a combination thereof), and atop transparent cathode layer. Light generated from the device isemitted through the top transparent electrode. This is commonly referredto as a top-emitting device.

LEDs employing quantum dots prepared by colloidal methods do not havethe constraints of LEDs using dots grown by high vacuum depositiontechniques (S. Nakamura et al., Electron. Lett. 34, 2435 (1998)), namelythe substrate does not need to be lattice matched to the LEDsemiconductor system. For example, the substrate could be glass,plastic, metal foil, or Si. Additionally colloidal quantum dots can becombined with a number of different semiconductor matrix materials,including organics. Forming quantum dot LEDs using these colloidaltechniques is highly desirably, especially if low cost depositiontechniques are used to deposit the LED layers.

As is well known in the art, two low cost ways for forming quantum dotfilms include depositing a colloidal dispersion of ternary core/shellnanocrystals 120 by drop casting or spin casting. Common solvents fordrop casting quantum dots are a 9:1 mixture of hexane:octane (C. B.Murray et al., Annu. Rev. Mater. Sci. 30, 545 (2000)). The organicligands 115 need to be chosen such that the quantum dot particles aresoluble in hexane. As such, organic ligands with hydrocarbon-based tailsare good choices, such as, the alkylamines. Using well-known proceduresin the art, the ligands coming from the growth procedure (TOPO, forexample) can be exchanged for the organic ligand 115 of choice (C. B.Murray et al., Annu. Rev. Mater. Sci. 30, 545 (2000)). When spin castinga colloidal dispersion of quantum dots, the requirements of the solventare that it easily spreads on the deposition surface and the solventsevaporate at a moderate rate during the spinning process. It was foundthat alcohol-based solvents are a good choice; for example, combining alow boiling point alcohol, such as, ethanol, with higher boiling pointalcohols, such as, a butanol-hexanol mixture, results in good filmformation. Correspondingly, ligand exchange can be used to attach anorganic ligand (to the quantum dots) whose tail is soluble in polarsolvents; pyridine is an example of a suitable ligand. The quantum dotfilms resulting from these two deposition processes are luminescent, butnon-conductive. The films are resistive since non-conductive organicligands separate the ternary core/shell nanocrystals 120. The films arealso resistive since as mobile charges propagate along the quantum dots,the mobile charges get trapped in the core regions due to the confiningpotential barrier of the semiconductor shell 110.

FIG. 4 schematically illustrates a way of providing an inorganiclight-emitting layer 150 that is simultaneously luminescent andconductive. The concept is based on co-depositing small (<2 nm),conductive inorganic nanoparticles 140 along with the ternary-core/shellnanocrystals 120 to form an inorganic light emitting layer 150. Asubsequent inert gas (Ar or N₂) anneal step is used to sinter thesmaller inorganic nanoparticles 140 amongst themselves and onto thesurface of the larger ternary-core/shell nanocrystals 120. Sintering theinorganic nanoparticles 140 results in the creation of a continuous,conductive polycrystalline semiconductor matrix 130. Through thesintering process this matrix is also connected to the ternarycore/shell nanocrystals 120 and forms a polycrystalline inorganic lightemitting layer. Therefore, the polycrystalline inorganic light emittinglayer is an annealed film of a colloidal dispersion of ternarycore/shell nanocrystals and semiconductor matrix nanoparticles. As such,a conductive path is created from the edges of the inorganic lightemitting layer 150, through the semiconductor matrix 130 and to eachternary-core/shell nanocrystal 120, where electrons and holes recombinein a light emitting ternary semiconductor nanocrystals 100. It shouldalso be noted that encasing the ternary-core/shell nanocrystals 120 inthe conductive semiconductor matrix 130 has the added benefit that itprotects the quantum dots environmentally from the effects of bothoxygen and moisture

Preferably, the inorganic nanoparticles 140 are composed of conductivesemiconductive material, such as, type IV (Si), III-V (GaP), or II-VI(ZnS or ZnSe) semiconductors. In order to easily inject charge into theternary-core/shell nanocrystals 120, it is preferred that the inorganicnanoparticles 140 be composed of a semiconductor material with a bandgap comparable to that of the semiconductor shell 110 material, morespecifically a band gap within 0.2 eV of the shell material's band gap.For the case that ZnS is the outer shell of the ternary-core/shellnanocrystals 120, then the inorganic nanoparticles 140 are composed ofZnS or ZnSSe with a low Se content. The inorganic nanoparticles 140 aremade by chemical methods well known in the art. Typical synthetic routesare decomposition of molecular precursors at high temperatures incoordinating solvents, solvothermal methods (O. Masala and R. Seshadri,Annu. Rev. Mater. Res. 34, 41 (2004)) and arrested precipitation (R.Rossetti et al., J. Chem. Phys. 80, 4464 (1984)). As is well known inthe art, nanometer-sized nanoparticles melt at much reduced temperaturesrelative to their bulk counterparts (A. N. Goldstein et al., Science256, 1425 (1992)). Correspondingly, it is desirable that the inorganicnanoparticles 140 have diameters less than 2 nm in order to enhance thesintering process, with a preferred size of 1-1.5 nm. With respect tothe larger ternary-core/shell nanocrystals 120 with ZnS shells, it hasbeen reported that 2.8 nm ZnS particles are relatively stable for annealtemperatures up to 350° C. (S. B. Qadri et al., Phys. Rev B60, 9191(1999)). Combining these two results, the anneal process has a preferredtemperature between 250 and 350° C. and a duration up to 60 minutes,which sinters the smaller inorganic nanoparticles 140 amongst themselvesand onto the surface of the larger ternary core/shell nanocrystals 120,whereas the larger ternary-core/shell nanocrystals 120 remain relativelystable in shape and size. It should be noted that the inorganicnanoparticles 140 can be either nanodots, nanorods, nanowires, or anyother higher dimensional nanoparticle, such that, in one dimension thelength scale of the nanoparticle is less than 2 nm and, as a result,enables the sintering of the nanoparticles during the 250-350° C. annealprocess.

FIG. 5 gives one example of an inorganic electroluminescent LED device200 that incorporates the light emitting layer 150 containingternary-core/shell nanocrystals 120. A substrate 160 supports thedeposited semiconductor and metal layers; its only requirements are thatit is sufficiently rigid to enable the deposition processes and that itcan withstand the thermal annealing processes (maximum temperatures of˜325° C.). It can be transparent or opaque. Possible substrate materialsare glass, silicon, metal foils, and some plastics. The next depositedmaterial is an anode 170. For the case where the substrate 160 is p-typeSi, an anode 170 needs to be deposited on the bottom surface of thesubstrate 160. A suitable anode metal for p-Si is Al. It can bedeposited by thermal evaporation or sputtering. Following itsdeposition, it is annealed at ˜430° C. for 20 minutes. For all of theother substrate types named above, the anode 170 is deposited on the topsurface of the substrate 160 (as shown in FIG. 5) and includes atransparent conductor, such as, indium tin oxide (ITO). The ITO can bedeposited by sputtering or other well-known procedures in the art. TheITO is typically annealed at ˜300° C. for 1 hour to improve itstransparency. Because the sheet resistance of transparent conductors,such as, ITO, are much greater than that of metals, a bus metal 190 canbe selectively deposited through a shadow mask using thermal evaporationor sputtering to lower the voltage drop from the contact pads to theactual device. Next is deposited the inorganic light emitting layer 150.As discussed above it can be drop or spin casted onto the transparentconductor (or Si substrate). Other deposition techniques, such as,inkjetting the colloidal quantum dot-inorganic nanoparticle mixture isalso possible. Following the deposition, the inorganic light emittinglayer 150 is annealed at a preferred temperature of 250-300° C. for15-45 minutes. Lastly, a cathode 180 metal is deposited over theinorganic light emitting layer 150. Candidate cathode 180 metals areones that form an ohmic contact with the material forming the inorganicnanoparticles 140. For example, for the case of ZnS inorganicnanoparticles 140, a preferred metal is Al. It can be deposited bythermal evaporation or sputtering, followed by a thermal anneal at 285°C. for 10 minutes. Those skilled in the art can also infer that thelayer composition can be inverted, such that, the cathode 180 isdeposited on the substrate 160 and the anode 170 is formed on theinorganic light emitting layer 150. For the case of Si supports, thesubstrate 160 is then n-type Si.

Additionally, substrate 160 can be rigid or flexible and can beprocessed as separate individual pieces, such as sheets or wafers, or asa continuous roll. Typical substrate materials include glass, plastic,metal, ceramic, semiconductor, metal oxide, semiconductor oxide,semiconductor nitride, or combinations thereof. Substrate 160 can be ahomogeneous mixture of materials, a composite of materials, or multiplelayers of materials. The substrate 160 can either be light transmissiveor opaque, depending on the intended direction of light emission.

A light transmissive substrate 160 is desirable for viewing the lightemission through the substrate 160. Transparent glass or plastic arecommonly employed in such cases. Using FIG. 5 as a reference, a bottomemitting inorganic light emitting device can be formed on the substrate160 that is transparent. The first electrode (either anode 170 orcathode 180) is deposited over the substrate 160 and is transparent. Thepolycrystalline inorganic light emitting layer 150 is then formed overthe transparent first electrode, and a second electrode (either cathode180 or anode 170), which is reflective, is formed over the inorganiclight emitting layer 150.

For applications where the light emission is viewed through the topelectrode, the transmissive characteristic of the bottom support isimmaterial, and therefore can be light transmissive, light absorbing orlight reflective. Substrates for use in this case include, but are notlimited to, glass, plastic, semiconductor materials, ceramics, andcircuit board materials. Again using FIG. 5 as a reference, a topemitting device can be formed using any substrate 160. A reflectivefirst electrode is then deposited over the substrate 160, the inorganiclight emitting layer 150 is formed over the first electrode, and atransparent second electrode is formed over the inorganic light emittinglayer 150. Additionally, it is possible to have viewable emission fromboth sides of the display, by using a transparent substrate 160 andforming both electrodes from transparent materials.

Both top emitting and bottom emitting devices can be eitherpassive-matrix or active-matrix devices, and as such can be consideredto be electronic displays. The term “electronic display” refers to adisplay wherein electronic entities control the intensity of thedifferent areas of the display. In order for a device to haveindependently controllable, separate light emitting areas, at least oneof the electrodes must be patterned. Whence, an inventive passive oractive matrix light emitting device includes a plurality ofindependently controlled light emitting elements, wherein at least onelight emitting element includes: a first patterned electrode; a secondelectrode opposed to the first electrode; and a polycrystallineinorganic light emitting layer, including ternary core/shellnanocrystals within a semiconductor matrix, formed between theelectrodes. The patterned electrodes can be controlled by either thinfilm electronic components, or by a driver circuit(s) formed externallyto the substrate. FIG. 6 illustrates an example of an off-panel driverand a series of horizontal and vertical electrodes in a passive-matrixdisplay. Alternatively, substrate 160 can be an active-matrix substratewith low-temperature polysilicon or amorphous-silicon thin filmtransistors (TFTs). Electronic components on substrate 160 are notlimited to transistors. Substrate 160 can contain other activeelectronic components such as thin film electronic components that arecomposed of crystalline, polycrystalline or amorphous semiconductormaterials. Such thin film electronic components include, but are notlimited to: TFTs, capacitors, diodes, switches and resistors.

One example of a passive matrix device is illustrated in FIG. 6. Aninorganic light emitting display device according to the presentinvention includes a substrate 160. Row electrodes 12 and columnelectrodes 14 formed on one side of the substrate 160 define row 18 andcolumn 19 of passive matrix pixel elements 13 where the row and columnelectrodes overlap. The row and column electrodes 12 and 14 provide dataand selection signals to an array 16 of passive matrix pixel elements13. The row electrodes 12 and column electrodes 14 are connected toelectrical contacts 44 and 45 respectively. Discrete data drivers 22 andselection drivers 23 are located around the periphery of the array 16and are electrically connected to the electrical contacts 44 and 45. Thediscrete data and selection drivers 22 and 23 are conventionalintegrated circuits formed on separate, discrete substrates (such assilicon). They can be separate from the substrate 160 as shown, orattached onto the same side of the substrate 160 as row and columnelectrodes 12 and 14. The discrete data drivers 22 and selection drivers23 drive the pixel elements 13 using a passive matrix control scheme andrespond to address and data control signals provided by a displaycontroller 30 through address, data, and control lines 24. The datavalues can be written into the data drivers 22 using conventional memorywriting techniques using the address, data and control lines 24.

Referring again to FIG. 6, the passive matrix pixel elements 13 containactive layers that emit light in response to an electric signal. Assuch, inorganic electroluminescent media 410 (FIG. 8) is placed betweenthe electrodes 12 and 14; the inorganic electroluminescent media 410includes the inorganic light emitting layer 150. Additionally, inorganicelectroluminescent media 410 may include inorganic charge transportlayers. When a light-emitting element is energized through one column 19and one row 18, the element at the column and row intersection isenergized and light is emitted. Light can be viewed either through thesubstrate or from the top depending on the materials used to constructthe passive matrix device.

There are many potential pixel designs for a bottom emitting activematrix device. A physical layout view of one design for inorganic lightemitting device 200 using amorphous silicon type TFTs is shown in FIG.7. The construction of the various circuit components such as a selecttransistor 320, a storage capacitor 330, and a power transistor 340 canbe seen in FIG. 7. The drive circuitry components are fabricated usingconventional integrated circuit and thin film transistor fabricationtechnologies. A select line 313 is formed in a first conductor layer. Apower line 311 and a data line 312 are formed in a second conductorlayer. An insulator is formed there in order to electrically isolatethese two conductor layers. This configuration permits the data linesand power lines to cross without electrically connecting thereby formingthe matrix of pixels. Electrical connections between features formed inthe different conductor layers are achieved by forming contact holes,also referred to as vias, through the insulator layers disposed betweenthe conductor layers. The term electrical connection is used in thisdisclosure to indicate a connection that enables the flow of electricalcurrent. This can be a direct physical connection of two conductiveelements. An electrical connection can have electrical resistance. Anelectrical connection can also be indirectly provided through othercircuit components such as transistors or diodes.

A portion of the select line 313 extends to form the gate of selecttransistor 320. Over this first conductor layer is a first insulatorlayer (not shown), which is also referred to as the gate insulatorlayer. Select transistor 320 is formed from a first semiconductor region321 using techniques well known in the art. The first terminal, whichcan be either the source or drain terminal, is formed from a portion ofdata line 312. A second terminal of select transistor 320, a terminal326, extends to form the second capacitor electrode of storage capacitor330 and also to electrically connect to a power transistor gateelectrode 343 of power transistor 340 through a contact hole 342. Thetransistors, such as select transistor 320, are shown as bottom gatetype transistors, however, other types such as top gate and dual-gatetransistors are also known in the art and can be employed. Similarly,power transistor 340 is formed in a second semiconductor region 341. Thefirst semiconductor region 321 and second semiconductor region 341 aretypically formed in the same semiconductor layer over the gate insulatorlayer. The semiconductor layer is composed of multiple sub-layers suchas an intrinsic, or undoped, sub-layer and a doped sub-layer. Thissemiconductor layer here is amorphous silicon but can also bepolycrystalline or crystalline or known semiconductor materials otherthan silicon, such as organic semiconductors and metal oxidesemiconductors. The power transistor gate electrode 343 of powertransistor 340 is formed in the first conductor layer. The firstterminal of power transistor 340 is formed from a portion of power line311, as shown. A second terminal 346 of power transistor 340 is formedin the second conductor layer. Storage capacitor 330 is formed between afirst capacitor electrode 333 formed in the first conductor layer andthe second capacitor electrode formed as a portion of terminal 326 asdescribed above. The gate insulator layer (not shown) is depositedbetween the first capacitor electrode and the second capacitorelectrode. The first capacitor electrode 333 is electrically connectedto power line 311 through a contact hole 332. Alternate configurationsare known in the art where the storage capacitor is not directlyconnected to the power line but is instead provided a separate capacitorline, which can be maintained at a different voltage level or the samevoltage level relative to the power line.

A lower electrode 381 of the inorganic light emitting device is formedfrom a third conductor layer formed over the first and second conductorlayers. A second insulator layer (not shown) is located between thelower electrode 381 and the second conductor layer. The lower electrode381 of the inorganic light emitting device is connected to powertransistor 340 through a contact hole 345 formed in this secondinsulator layer.

Lower electrode 381 serves to provide electrical contact to theinorganic electroluminescent media (not shown) of the inorganic lightemitting diode. Over the perimeter edges of the lower electrode 381, aninter-pixel insulator layer (not shown) can also be formed to cover theedges of the electrodes and reduce shorting defects as is known in theart. Examples of such inter-pixel insulator layers can be found in U.S.Pat. No. 6,246,179.

A cross-sectional illustration of the device of FIG. 7 along line X-X′is shown in FIG. 8. In this cross-sectional view the position of theinsulating substrate 160 as well as the positions of a first insulatorlayer 401 (also referred to as the gate insulator layer) and a secondinsulator layer 402 can be seen. These insulator layers are shown assingle layers but can actually include several sub-layers of differentinsulating materials. The construction of the amorphous silicon powertransistor 340 is shown. The second semiconductor region 341 is shownwith an intrinsic sub-layer 341 a and a doped sub-layer 341 b.

The placement of an inter-pixel insulator 403 over the edges of lowerelectrode 381 is shown. Over lower electrode 381, the inorganicelectroluminescent media 410 is formed. The inorganic electroluminescentmedia 410 includes all of the layers between the anode and cathode. InFIG. 8, the inorganic electroluminescent media 410 is shown as a singlelayer, but it is typically composed of a plurality of sub-layers such asa polycrystalline inorganic light-emitting layer and one or moreinorganic charge transport layers. Above the inorganicelectroluminescent media 410, an upper electrode 420 is formed. Upperelectrode 420 is typically common in such active matrix arrangements andserves to provide an electrical connection to the second voltage level.The lower electrode 381 and upper electrode 420 serve as spaced apartelectrodes which provide electrical current to the inorganicelectroluminescent media 410 disposed between the electrodes. Whenelectrically stimulated, the inorganic electroluminescent media 410above the lower electrode 381 in the area defined by the opening of theinter-pixel insulator 403 will emit light 450. Light 450 is shown asexiting the bottom of the device (through the substrate 160). Thisconfiguration is known as a bottom-emitting configuration. This requiresthat lower electrode 381 be at least partially transparent. As such,lower electrode 381 is commonly constructed of materials such as indiumtin oxide (ITO), indium zinc oxide (IZO), or thin (less than 25 nm)layers of metal such as aluminum or silver, or combinations, thereof.The upper electrode 381 is typically reflective in such a configuration,being constructed at least in part of a reflective metals such asaluminum, aluminum alloys, silver or silver alloys. The oppositeconfiguration is known in the art where light exits through the upperelectrode, the direction opposite of the substrate. This oppositeconfiguration is known as a top emitter configuration. In thisconfiguration, the light transmissive and reflective properties of theupper and lower electrodes respectively are reversed from that of thebottom emitter configuration. The cross-sectional view in FIG. 9illustrates a top emitter configuration consistent with the presentinvention. FIG. 9 can be understood within the context of thedescription of FIG. 8. Although not shown, it should be understood byone skilled in the art that additional pixel layout arrangements areapplicable to the current invention, both for amorphous silicon and lowtemperature poly-silicon transistors.

The ternary-core/shell quantum dots of this invention can be used toform monochrome, multi-color or full-color displays. The term“multi-color” describes a display panel that is capable of emittinglight of a different hue in different areas. In particular, it isemployed to describe a display panel that is capable of displayingimages of different colors. These areas are not necessarily contiguous.The term “full color” is commonly employed to describe multi-colordisplay panels that are capable of emitting in at least the red, green,and blue regions of the visible spectrum and displaying images in anycombination of hues. The complete set of colors that can be generated bya given display is commonly called the color gamut of the display. Thered, green, and blue colors constitute the three primary colors fromwhich all other colors can be generated by appropriate mixing. However,the use of additional colors to extend the color gamut is possible.Additionally, there are practical applications for displays that emitoutside of the visible range. Therefore, the ternary-core/shell quantumdots of each light emitting element or device can be selected to have anemission wavelength that suites the application. These wavelengths canbe ultraviolet, blue, cyan, green, yellow, magenta, red, or infrared incharacteristic, or any combination thereof.

The term “pixel” is employed in its art-recognized usage to designate anarea of a display panel that can be stimulated to emit lightindependently of other areas. The terms “light emitting element” and“independently controlled light emitting element,” for the purposes ofthis discussion is synonymous with pixel. It is also noted that nophysical size requirements should be inferred from either term: pixel orlight emitting element. A device may consist of a single largelight-emitting element, millions of small light-emitting elements, orany practical configuration in between. It is recognized that infull-color systems, several pixels of different colors will be usedtogether to generate a broad range of colors, and a viewer can term sucha group as a single pixel. For the purposes of this disclosure, such agroup will be considered several different light-emitting elements orpixels.

Inorganic light emitting devices of this invention can have broadbandemission. Broadband emission is light that has significant components inmultiple portions of the visible spectrum, for example, blue and green.Broadband emission can also include light being emitted in the red,green, and blue portions of the spectrum in order to produce whitelight. White light is that light that is perceived by a user as having awhite color, or light that has an emission spectrum sufficient to beused in combination with color filters to produce a practical full colordisplay. The term “white light-emitting” as used herein refers to adevice that produces white light internally, even though part of suchlight can be removed by color filters before viewing. Accordingly, whitelight-emitting inorganic light emitting devices of this invention can beused for lighting applications as solid-state light sources, forexample, as lamps. In display applications, such a white light-emittinginorganic light-emitting device can be used as a display backlight for alight-gating device that modulates the light to form an image. Onepractical example of this would be a display backlight in a liquidcrystal display (LCD).

Electroluminescent applications such as displays and lighting use theensemble properties of the quantum dots in the device. There are alsoelectroluminescent applications that only utilize the properties of asingle quantum dot. For example single molecule LEDs (or lasers) can beeither single quantum dots embedded within an etched mesoscopicheterojunction (J. Vuckovic et al., Appl. Phys. Lett. 82, 3596 (2003)),or can be fabricated so that all of the active layers of the LED (orlasers) are contained within a single nanocrystal (R. Agarwal and C. M.Lieber, Appl. Phys. A: Mater. Sci. Proc. 85, 209-215 (2006)). Theability to generate single photons (using single photon LEDs) at awell-defined timing or clock is crucial for practical implementation ofquantum key distribution (N. Gisin et al., Rev. Mod. Phys. 74, 145(2002)), as well as for quantum computation (E. Knill et al., Nature409, 46 (2001)) and networking based on photon qubits (quantum bits).Three different criteria are taken into account when evaluating thequality of a single photon source: high efficiency, small multiphotonprobability (measured by the second order coherence function, g⁽²⁾(0)),and quantum indistinguishability. For some quantum cryptographyimplementations, such as, the BB84 protocol (N. Gisin et al., Rev. Mod.Phys. 74, 145 (2002), high efficiency and small g⁽²⁾(0) are required,but quantum indistinguishability is not necessary. On the other hand,for almost all other applications in quantum information systems, suchas, linear optics quantum computation, LOQC (E. Knill et al., Nature409, 46 (2001)), the photons need to undergo multiphoton interference,and as a result, quantum indistinguishability is required.

Single photon LEDs have been constructed that are optically pumped (C.Santori et al., Nature 419, 594 (2002)) by lasers and electricallypumped (Z. Yuan et al., Science 295, 102 (2002)), where in the majorityof cases the emissive species has been self-assembled quantum dots. Thetypical way for improving the efficiency of the devices is to place thequantum dots within a microcavity configuration, where the best resultsare obtained for confinement in all three dimensions. As a result of theconfinement, the IQE of the device is improved (due to the Purcelleffect) and the collection efficiency is greatly enhanced (due to thelarge reduction in the number of available output modes). Associatedwith the improvement in the IQE is the large reduction in the quantumdot radiative lifetime (about a factor of 5), down to around 100-200 ps.This reduction in radiative lifetime also results in improvements in thequantum indistinguishability (A. J. Shields, Nature Photon. 1, 215(2007)). Consequently, a key to both high efficiency and quantumindistinguishability is a short radiative lifetime. As such, since theternary-core/shell quantum dots of the present invention have greatlyreduced radiative lifetimes compared to typical colloidal quantum dots,it is an advantage to use them in single photon LED devices, eitheroptically or electrically pumped. Another useful aspect of the inventedternary-core/shell quantum dots is their lack of blinking. Naturally,the usefulness of a single photon LED source is greatly reduced if itturns off due to unwanted blinking behavior. With regard to electricallypumped single photon LEDs, a preferred optoelectronic device of thepresent invention has two spaced apart electrodes with a single ternarycore/shell nanocrystal 120 disposed between the two spaced apartelectrodes. As is well known in the art, the electrically pumped singlephoton LED containing a single ternary core/shell nanocrystal 120 canalso include n- and p-transport layers, conductive organic or inorganicmatrix material surrounding the single nanocrystal, distributed braggreflectors, and other well known enhancements in order to improve theIQE and collection efficiency of the device. For optically pumped singlephoton LEDs, a preferred embodiment is an optical cavity containing atleast one layer including a single ternary core/shell nanocrystal 120 inan appropriate matrix and a light source for optically exciting theternary core/shell nanocrystal 120 so as to cause the emission of UV,visible, or infrared light. The matrix material can be inorganic,organic, or combinations thereof. It is preferred that the light sourceis a laser. As is well known in the art, the optically pumped singlephoton LED containing a single ternary core/shell nanocrystal 120 canalso include dielectric mirrors, photonic lattices, spacer layers, andother well known enhancements in order to improve the IQE and collectionefficiency of the device. In sum, both the non-blinking and shortradiative lifetime properties of the invented ternary-core/shell quantumdots lead to their adventitious use in single photon LED devices (eitheroptically or electrically pumped) for quantum cryptography and quantumcomputing applications.

The following examples are presented as further understandings of thepresent invention and are not to be construed as limitations thereon.

Inventive Example I-1 Preparation of the Inventive Ternary Core/ShellNon-Blinking Nanocrystals, Cd_(x)Zn_(1-x)Se/ZnSe

All synthetic routes were carried out using standard airless procedureswith a dry box and a Schlenk line. The first step in creating theternary cores was to form CdSe cores. Typically, 0.0755 g of TDPA(1-tetradecylphosphonic acid), 4 g of pre-degassed TOPO(trioctylphosphine oxide), and 2.5 g of HDA (hexadecylamine) were addedin a three-neck flask. The mixture was degassed at 100° C. for half anhour. The stock solution of 1 M TOPSe was prepared by dissolving of 0.01mol selenium in 10 ml TOP (trioctylphosphine). 1 ml of TOPSe was addedto the flask and the mixture was heated to 300° C. The cadmium stocksolution (0.06 g of CdAc₂ in 3 ml TOP) was quickly injected undervigorous stirring resulting in nucleation of CdSe nanocrystals, afterwhich time the temperature was set at 260° C. for further growth. After5-10 min, the heating was removed and the flask was allowed to cool toroom temperature.

2.5 ml of the as-prepared crude CdSe cores was reheated to 300° C. inhalf an hour. In a drybox, two solutions were prepared. One consisted of0.14 ml of 1 M ZnEt₂ (in hexane) and 0.56 ml of TOP; the other consistedof 0.14 ml of 1 M TOPSe (in TOP) and 0.56 ml of additional TOP. Bothsolutions were loaded into a 1 ml syringe respectively. As soon as thetemperature of the core crude solution reached 300° C., 0.35 ml of theZnEt₂ solution was injected from the syringe into the heated solution,followed by the injection of 0.35 ml TOPSe solution in 20 seconds. Theabove procedure was repeated at time intervals of 20 seconds till thecontents of both syringes were emptied. After the addition, the reactionmixture was heated for 5 more minutes, and then heat was removed to stopthe reaction.

The final step in the process was shelling of the CdZnSe ternary cores.A three-neck reaction flask with as-prepared crude Cd_(x)Zn_(1-x)Secores was heated to 190° C. The solution of ZnEt₂ (1 M, 0.625 ml) andTOPSe (1M, 1.25 ml) in 1 ml TOP was slowly added dropwise under vigorousstirring. After the addition the temperature was lowered to 180° C. andthe solution was left to stir for another hour to form annealedCd_(x)Zn_(1-x)Se/ZnSe nanocrystals.

Inventive Example I-2 Preparation of the Inventive Ternary Core/ShellNon-Blinking Nanocrystals, Cd_(x)Zn_(1-x)Se/ZnSeS

All synthetic routes were carried out using standard airless procedureswith a dry box and a Schlenk line. The first step in creating theternary cores was to form CdSe cores. In a three-neck flask, 0.2 mmol ofCdO and 0.5 g of stearic acid were heated to 180° C. until the mixturewent clear. Inside of a dry box, 3 ml of HDA and 6 ml of TOPO were addedto the mixture. On a Schlenk line the mixture was heated to 310° C.under vigorous stirring, whereupon 1 ml of 1 M TOPSe was injected. Thetemperature was then lowered to 290-300° C. and stirred for anadditional 10 minutes.

Next a ZnSe shell was formed on the CdSe cores. After cooling the corecrude solution back to room temperature, it was reheated to 190° C. In asyringe was added 260 μl of 1 M diethylzinc in hexane, 260 μl of 1MTOPSe, and 2 ml of TOP. The contents of the syringe were then added tothe CdSe core crude solution at a rate of 10 ml/hr. After the additionthe mixture temperature was lowered to 180° C., in order to anneal theresulting ternary cores for 45-90 minutes. After the 180° C. anneal, themixture temperature was taken back to room temperature. A second annealwas then performed for 30 minutes at 300° C. to create the ternary corenanocrystals containing a gradient in the alloy composition.

The final step in the process was shelling of the CdZnSe ternary coreswith ZnSeS (ZnSe_(0.33)S_(0.67) in the example below). In a new 3-neckflask was added 1.5 ml of the CdZnSe crude cores, 4 ml of TOPO, and 3 mlof HDA, followed by heating the mixture to 190° C. In a syringe wasadded 804 μl of 1 M diethylzinc in hexane, 268 μl of 1M TOPSe, 536 μl of0.25M bis(trimethylsilyl)sulfide in hexane, and 2.5 ml of TOP. Thecontents of the syringe were then added to the CdZnSe core crudesolution at a rate of 10 ml/hr. After the addition the mixturetemperature was lowered to 180° C., in order to anneal the resultingternary cores for 45-90 minutes.

FIG. 10 shows a TEM (transmission electron microscopy) image of theternary core/shell nanocrystals of this example. It should be noted thatthe emissive nanocrystals were quantum rods with an aspect ratio ofapproximately 2.5:1. FIG. 11 shows a STEM (scanning TEM) image of anisolated ternary core/shell nanocrystal of this example. The image wastaken at a magnification of 5 million. The nanocrystal was imaged alongthe (−2 1 0 0) wurtzite axis. The image shows that the nanocrystal has awurtzite lattice structure in the center of the nanorod (as evidenced bythe waviness of the lattice fringes) and at the ends of the nanorod hasa cubic (or zincblende) lattice as evidenced by the alignment of thelattice fringes. STEM images showing the lattice transition fromwurtzite at the center of the nanocrystal to cubic (zincblende) at thesurface of the nanocrystal were also obtained for core ternarynanocrystals (thus without a outer shell) of this example.

Single Molecule Blinking and Anti-Bunching Measurements

Standard single molecule blinking and anti-bunching measurements wereperformed on the ternary core/shell nanocrystals of examples I-1 andI-2. In addition for comparison, prior art CdTe nanocrystals (80%quantum yield) from Quantum Dot Corporation were also measured. For bothsingle molecule measurements, standard procedures were followed forcreating very dilute films of the nanocrystals on quartz coverslips. Theoptical measurements were made using a Nikon confocal microscope excitedby a 532 nm continuous green laser. The laser excitation was focused toa diffraction limited spot of ˜400 nm by an oil immersion objective (1.5NA). The emission from the sample was collected through the sameobjective, with the 532 nm light rejected by a filter. The emission wasthen directed into a silicon avalanche photodiode (SAPD). Thefluorescence intensity versus time trace was obtained by feeding theSAPD output into a TTL multichannel scaler with integration times of1-30 ms/bin. The laser power density used to excite all of thenanocrystals (both inventive and prior art) was varied from ˜0.1-10kW/cm². The anti-bunching measurements were performed using aHanbury-Brown and Twiss setup (R. Hanbury et al., Nature 177, 27 (1956))with a 50/50 beamsplitter and two single-photon counting SAPDs. The twoSAPDs were connected to the start and stop inputs of a time-to-amplitudeconverter, whose output was stored in a time correlated photon countingcard.

FIGS. 12A and 12B give examples of the fluorescence time traces for thecore/shell ternary nanocrystals of example I-1. For the data shown inFIG. 12A the laser power density was ˜1 kW/cm² (30 ms time bins), whilefor the data of FIG. 12B, the laser power density was ˜10 kW/cm² (10 mstime bins). As can be seen, the ternary nanocrystals have on-times of˜10 minutes. In fact, the ternary nanocrystals turn off not due toblinking phenomena, but due to being photo-bleached. As a result theternary nanocrystals with good photostability characteristics had ontimes up to several hours (for the 1 kW/cm² excitation density). It wasalso verified that blinking did not occur on a very fast time scale,since similar time traces were obtained for time bins as small as 1 ms.At the higher laser power excitation density of 10 kW/cm², FIG. 12Bshows that the ternary dots can have on-times of ˜10 minutes (beyond 10minutes, all of the ternary dots become photo-bleached at the 10 kW/cm²excitation density). The ternary dots from example I-2 also had verylong on-times (>10 minutes); in addition they turned off as a result ofbeing photo-bleached.

For comparison FIG. 13 shows the fluorescence time trace of the priorart CdTe nanocrystals at a laser power excitation density of 10 kW/cm²,where the collection times bins were 10 ms. The time trace behaviorshown in FIG. 13 is typical of nanocrystals films reported in theliterature, where the highest reported on-times are ˜1 minute. As such,the inventive ternary core/shell nanocrystals have significantlydifferent single molecule fluorescence intermittency behavior comparedto prior art nanocrystals previously reported in the literature.

FIGS. 14A and 14B give representative second-order correlationfunctions, g⁽²⁾(τ) for the core/shell ternary nanocrystals of exampleI-1 and the prior art CdTe nanocrystals, respectively. The correlationfunction for the ternary nanocrystals shows unambiguous anti-bunchingbehavior at τ=0. This is especially important for the inventivenanocrystals since it demonstrates that the non-blinking behavior is dueto isolated nanocrystals. As can be seen the radiative lifetime of thecore/shell ternary nanocrystals (4-5 ns, on average) was significantlylower than that for the prior art CdTe nanocrystals (20 ns on average).For comparison, radiative lifetimes (derived by anti-bunchingmeasurements) for quantum rods can range from 20-200 ns, while lifetimesfor self-assembled quantum dots are in the 1-2 ns range. For the ternarycore/shell nanocrystals of example I-2, photo-bleaching issues led todifficulties in extracting a radiative lifetime using anti-bunchingmeasurements.

Quantum Yield Measurements

Absolute quantum yield measurements (using an integrating sphere) weremade for dense nanocrystal films composed of the ternary core/shellnanocrystals from examples I-1 and I-2. For the I-1 case, a standardligand exchange was performed to remove the TOPO, HDA, and TOP ligandsand replace them solely with HDA. Concentrated dispersions of the HDAterminated nanocrystals were drop cast out of toluene onto glass slides.The resulting absolute quantum yield was ˜75%. In comparison therelative quantum yield of the corresponding dispersion was ˜80%. For theI-2 case, a ligand exchange was performed to replace the growth ligandswith pyridine. Once more a concentrated dispersion was formed (ethanolsolvent) and drop cast onto glass slides. The resulting absolute quantumyields of the films were ˜40%, while that for the correspondingdispersion was ˜36%. In both cases, there is no degradation (withinexperimental error) in quantum yield in going from solution measurementsto dense film measurements. In comparison, it is well known that typicalnanocrystals suffer at least a factor of 2 or 3 drop-off in quantumyield in going from solution to film (Achermann et al., Nano Lett 6,1396 (2006)).

In summary, the ternary core/shell nanocrystals of examples I-1 and I-2exhibit no blinking (with on times greater than hours), very shortradiative lifetimes (4-5 ns) that are reminiscent of self-assembledquantum dots, and resistance to proximity quenching in dense nanocrystalphosphor films.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   10 substrate-   11 LED-   12 row electrode-   13 pixel element-   14 column electrode-   15 EL unit-   16 array-   17 first electrode-   18 rows-   19 column-   20 second electrode-   22 data driver-   23 selection driver-   24 control lines-   30 controller-   31 semiconductor matrix-   33 light-emitting layer-   35,37 charge transport layers (optional)-   44 electrical contacts-   45 electrical contacts-   100 ternary semiconductor nanocrystal-   110 semiconductor shell-   115 organic ligands-   120 ternary core/shell nanocrystal-   130 semiconductor matrix-   135 ternary surface region-   140 inorganic nanoparticles-   145 ternary center region-   150 inorganic light emitting layer-   160 substrate-   170 anode-   180 cathode-   190 bus metal-   200 inorganic light emitting device-   311 power line-   312 data line-   313 select line-   320 select transistor-   321 first semiconductor region-   326 terminal-   330 capacitor-   332 contact hole-   333 capacitor electrode-   340 power transistor-   341 second semiconductor region-   341 a intrinsic sub-layer-   341 b doped sub-layer-   342 contact hole-   343 power transistor gate electrode-   345 contact hole-   346 terminal-   381 lower electrode-   401 first insulating layer-   402 second insulating layer-   403 interpixel insulator-   410 inorganic electroluminescent media-   420 upper electrode-   450 light

1. An optoelectronic device comprising: (a) two spaced apart electrodes;and (b) at least one layer containing ternary core/shell nanocrystalsdisposed between the spaced electrodes and having ternary semiconductorcores containing a gradient in alloy composition and wherein the ternarycore/shell nanocrystals exhibit single molecule non-blinking behaviorcharacterized by on times greater than one minute or radiative lifetimesless than 10 ns.
 2. The optoelectronic device of claim 1 wherein thedevice is a display backlight or a solid-state light source.
 3. Aninorganic light emitting device including a plurality of independentlycontrolled light emitting elements, wherein at least one light emittingelement comprises: a first patterned electrode; a second electrodeopposed to the first electrode; and a polycrystalline inorganic lightemitting layer comprising ternary core/shell nanocrystals within asemiconductor matrix formed between the electrodes, wherein the ternarycore/shell nanocrystals have ternary semiconductor cores containing agradient in alloy composition and exhibit single molecule non-blinkingbehavior characterized by on times greater than one minute or radiativelifetimes less than 10 ns.
 4. The inorganic light emitting device ofclaim 3, further including thin film electronic components formed on thesubstrate or a driver circuit formed externally to the substrate forindependently controlling signals applied to the patterned firstelectrodes.
 5. The inorganic light emitting device of claim 4 whereinthe thin film electronic components are composed of crystalline,polycrystalline or amorphous semiconductor materials.
 6. The inorganiclight emitting device of claim 3 wherein the device is a displaybacklight, multi-color display, full color display, monochrome displayor lighting device.
 7. The inorganic light emitting device of claim 3wherein the independently controlled light emitting elements emit lightof different colors.
 8. The inorganic light emitting device of claim 3,wherein the ternary core/shell nanocrystals of each light emittingelement have an emission wavelength selected from an ultraviolet, blue,cyan, green, yellow, magenta, red, or infrared emission wavelength, or acombination thereof.
 9. The inorganic light emitting device of claim 3wherein the polycrystalline inorganic light emitting layer is anannealed film of a colloidal dispersion of ternary core/shellnanocrystals and semiconductor matrix nanoparticles.
 10. A single photonoptoelectronic device comprising: (a) two spaced apart electrodes; and(b) a single ternary core/shell nanocrystal disposed between the twospaced apart electrodes and having a ternary semiconductor corecontaining a gradient in alloy composition and exhibiting singlemolecule non-blinking behavior characterized by on times greater thanone minute or radiative lifetimes less than 10 ns.
 11. Theoptoelectronic device of claim 10, wherein the device is included in aquantum computing or a quantum cryptography device.
 12. An opticaldevice comprising: (a) at least one layer containing ternary core/shellnanocrystal(s) wherein the ternary core/shell nanocrystal(s) haveternary semiconductor cores containing a gradient in alloy compositionand exhibit single molecule non-blinking behavior characterized by ontimes greater than one minute or radiative lifetimes less than 10 ns;and (b) a light source for optically exciting the ternary core/shellnanocrystal(s) so as to cause emission of light from the ternarycore/shell nanocrystal(s).
 13. The optical device of claim 12 whereinthe device is a single photon optical device, and wherein the at leastone layer comprises a single ternary core/shell nanocrystal and thelight source is a laser.
 14. The single photon optical device of claim13, wherein the device is included in a quantum computing or a quantumcryptography device.
 15. The optical device of claim 12, wherein thelight source is an inorganic LED, an organic LED, a laser, or a compactfluorescent lamp.
 16. The optical device of claim 12, wherein theternary core/shell nanocrystal(s) have an emission wavelength selectedfrom an ultraviolet, blue, cyan, green, yellow, magenta, red, orinfrared emission wavelength, or a combination thereof.
 17. A systemincluding a marker actuable by radiation and used to detect a givenanalyte, comprising: (a) a ternary core/shell nanocrystal, having aternary semiconductor core containing a gradient in alloy compositionand exhibiting single molecule non-blinking behavior characterized by ontimes greater than one minute or radiative lifetimes less than 10 ns;and (b) a molecule conjugated with the ternary core/shell nanocrystaland having a binding affinity for the analyte.
 18. The system of claim17 further including: (c) a medium containing the given analyte, and;(d) a light source for illuminating the marker with radiation thatcauses the emission of light from the conjugated ternary core/shellnanocrystal that is analyzed to determine the presence of the analyte.